Printing mechanism

Abstract

A printing mechanism having an engaging body that is rotatable between an engaging position, in which it retains a printing roller in a position facing a thermal printing head, and a disengaging position wherein it enables the printing roller to be removed; a reversible drive shaft rotating in one direction rotates the printing roller and rotating in the opposite direction moves the engaging body to the disengaging position, owing to a unidirectional joint that connects the drive shaft to the engaging body only when the drive shaft rotates in an opposite direction.

The invention claimed is: 
     
       1. Printing mechanism comprising:
 a frame; 
 a thermal printing head arranged on said frame; 
 a printing roller having an operating arrangement wherein it is rotatably coupled in a removable manner with said frame and faces said printing head to achieve in use a printing and advancement step wherein a printing support advances interposed between said roller and printing head; 
 an engaging arrangement rotatably coupled with said frame with the possibility of rotating around a rotation axis adopting at least one active position wherein it engages said printing roller with said frame in said operating arrangement and at least one inactive position wherein it leaves said printing roller free to be removed from said frame; 
 a motor arranged on said frame to rotate said printing roller at least in one rotation direction, said motor having a drive shaft with reversible rotation motion in a first rotation direction and in a second rotation direction opposite the first; 
 a transmission arrangement for transmitting the motion of said drive shaft at least in said first rotation direction to said printing roller to drag the printing support interposed between said roller and printing head; 
 a unidirectional joint arrangement arranged for transmitting the motion of said drive shaft in said second rotation direction to said engaging arrangement to rotate said engaging arrangement from said active position to said inactive position and enable said printing roller to be removed, and in order not to transmit the motion of said drive shaft in said first rotation direction to said engaging arrangement to maintain said printing roller in said operating arrangement. 
 
     
     
       2. Printing mechanism according to  claim 1 , wherein said unidirectional joint arrangement is coaxial with said rotation axis. 
     
     
       3. Printing mechanism according to  claim 1 , wherein said unidirectional joint arrangement comprises a unidirectional bearing. 
     
     
       4. Printing mechanism according to  claim 1 , wherein said engaging arrangement comprises a rotatable body bearing at least one engaging arm that, in said active position, closes in the upper part a seat for a pin of said printing roller to retain the pin in the seat. 
     
     
       5. Printing mechanism according to  claim 4 , wherein said rotatable body has at least two engaging arms operating in two seats for two pins at the two opposite ends of the axis of said printing roller. 
     
     
       6. Printing mechanism according to  claim 4 , wherein said rotatable body has a gripping zone for facilitating the rotation of said rotatable body, said gripping zone being arranged next to said transmission arrangement above said engaging arm and protruding upwards in a removal direction of said printing roller. 
     
     
       7. Printing mechanism according to  claim 1 , wherein said transmission arrangement comprises gears having at least a first gear wheel that is coaxial with said rotation axis. 
     
     
       8. Printing mechanism according to  claim 7 , wherein said transmission arrangement comprises at least a second gear wheel that is coaxial with said printing roller and engages with said first gear wheel when said printing roller is in said operating arrangement. 
     
     
       9. Printing mechanism according to  claim 8 , wherein said second gear wheel is integral with said printing roller so it is removed from the printing mechanism together with said printing roller. 
     
     
       10. Printing mechanism according to  claim 1 , made as a block that integrates said frame, said printing head, said printing roller, said engaging arrangement, said motor, said transmission arrangement and said unidirectional joint arrangement, said block forming a separate unit intended to be inserted into a printing device; said frame extending in length in a direction parallel to the axis of said printing roller, the dimension in length of said printing roller being at least two or three times greater than each of the other two dimensions in width and height, the length dimension being optionally comprised between 50 and 250 mm; said thermal printing head having an electric contact element arranged on said frame for connection with at least an electronic control device outside said printing mechanism.